Gas phase migration of C-14 through barrier materials applicable for use in a high-level nuclear waste repository located in tuff

Miscellaneous · Sat Dec 31 00:00:00 EST 1988

OSTI ID:138638

Bauer, L R

A study of the movement of {sup 14}CO{sub 2} through proposed barrier media has been conducted. Diffusion coefficients for crushed tuff, bentonite and a 90:10% by wt. mixture of crushed tuff and bentonite were measured for two diffusion lengths. The ability of {sup 14}CO{sub 2} to penetrate a microsilica-containing portland cement mortar proposed for repository use was also examined. The specimens were subjected to uniaxially-applied compressive loads prior to the diffusion tests to simulate the onset of environmentally-induced microcracks. Based on these experiments, the apparent diffusion coefficients for the soil-based media were as follows: crushed tuff, 1.73 {plus_minus} 0.26 {times} 10{sup {minus}2} cm{sup 2}/s; bentonite, 1.56 {plus_minus} 0.61 {times} 10{sup {minus}2}/s; and the crushed tuff/bentonite mixture, 1.77 {plus_minus} 0.13 {times} 10{sup {minus}2} cm{sup 2}/s. These values correspond roughly to breakthrough times of 5 and 10-15 min respectively for the 6.5- and 23-cm thicknesses studied. With respect to the mortar studies, the penetration of {sup 14}CO{sub 2} through 1-cm thick microfractured discs was, in all cases, limited to the upper 1 mm of the cement surfaces. Serial sampling of the diffusion cells and pH testing of the cement surfaces indicated that the {sup 14}CO{sub 2} was consumed by the reaction of CO{sub 2} with free Ca(OH){sub 2} in the cement to form calcite (CaCO{sub 3}). The formation of the calcite apparently acted as a chemical and/or physical barrier to {sup 14}CO{sub 2} migration. Only when a disc was completely fractured could significant penetration of {sup 14}CO{sub 2} be observed. These results may have implications for the ability of a repository to comply with the applicable regulatory release limits for C-14.

• Research Organization: Purdue Univ., Lafayette, IN (United States)
• OSTI ID: 138638
• Resource Relation: Other Information: TH: Thesis (Ph.D.); PBD: 1988
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
BENTONITE
RADIONUCLIDE MIGRATION
CARBON DIOXIDE
PORTLAND CEMENT
TUFF
ADSORPTION
CALCITE
CALCIUM CARBONATES
CALCIUM HYDROXIDES
CARBON 14
CHEMICAL REACTIONS
COMPRESSION
DIFFUSION
FRACTURES
MATERIALS RECOVERY
MIXTURES
PERMEABILITY
PH VALUE
RADIOACTIVE WASTE DISPOSAL
RADIOACTIVE WASTE FACILITIES
SEALS
SYNTHESIS
THICKNESS
TIME DEPENDENCE
Yucca Mountain Project